This invention relates to a separable electrical connector module and, more particularly, to a module of this type that includes a bore contact and coupled thereto a piston upon which gas generated during a fault-closing operation acts to drive the bore contact toward a mating rod contact, thereby to facilitate fault-closing.
In typical prior art designs of such modules, the piston has been made of copper, and it is adapted to slide within a container tube that is made of aluminum. A body of electrical insulation is molded or cast about the container tube; and the aluminum of the container tube provides high strength, enabling the container tube to withstand the high pressures usually associated with such molding or casting. The use of aluminum for the container tube also provides excellent compatibility with the insulating material, particularly when the insulating material is an epoxy compound such as used for integrated bushings. Examples of processes that have been used for incorporating the insulation are injection molding, compression molding, pressure gelation molding, and liquid casting.
Another feature of the above-described typical prior art design is that the aluminum container tube usually contains a thickened end wall that has a threaded opening therein for receiving an externally-threaded copper conductor. Electric current entering the module through the copper conductor follows a path that extends through the mating threads of the conductor and the container tube, into the aluminum container tube, and then into the copper piston to the bore contact.
Because of oxide formation and the relatively high resistance of a bare aluminum-to-copper connection, it has been customary to tin-plate the aluminum container tube where it is to contact the threaded conductor and the piston. However, there have been a number of problems associated with this tin-plating. Tin-plating aluminum, especially a long tube with an end wall containing a threaded opening (such as the container tube), has proven to be difficult and expensive. It has been especially difficult to provide a good tin-plate coating on the threads of the opening. An excessive amount of plating on these threads interferes with proper mechanical mating of the conductor module and the threaded conductor, while the absence of adequate plating has led to electrical problems under high current or load-cycling conditions.
The sliding connection between the piston and container tube has also had problems. When both the copper piston and the surrounding cylinder portion of the aluminum container tube are tin-plated, the sliding contact between piston and cylinder is one of tin on tin, which leads to high drag forces and material galling, both of which can result in undesirably slow piston-response during fault-closing operations.